There are many examples of underwater devices that have exhaust systems that expel the exhaust air or mixed gases into the surrounding water during their normal functions. One example of this is the Second Stage Regulator that SCUBA divers use while diving.
Some SCUBA diving setups may include a tank of compressed air or mixed gases that is worn by the diver, a first stage regulator attached to the tank that reduces the compressed air pressure form 3000 psi to around 150 psi, a hose that connects the first and second stage regulators, and a second stage regulator that is held in the diver's mouth that may reduce the pressure from 150 psi to ambient pressure and supply it to the diver upon demand.
Some of the components of the SCUBA second stage regulator may include: the regulator housing, a flexible diaphragm that collapses inwardly during the inhalation cycle against a small lever that activates an inhalation valve, thereby supplying the diver with air, an exhaust valve used as a one way valve to allow the exhaust air or gases to escape the regulator housing during the exhalation cycle, a bubble deflector to guide the exhaust bubbles out of the way of the diver's vision, and a mouth piece to seal out the surrounding water and to hold the regulator assembly in the diver's mouth.
The exhaust air or gases that are exiting the SCUBA second stage regulator may travel through an opening in the wall of the regulator housing. An exhaust valve may be mounted on the outside covering this opening, and may be used as a one-way valve to control the direction of flow of the exhaust gases. The circular opening may have one or more cross bars that go from one side of the opening to the other to be used as a mounting area for the exhaust valve and to help prevent the exhaust valve from collapsing inwardly when there is a negative pressure experienced.
Exhaust valves may be made from a molded flexible rubber or silicone and may be usually in round disk or mushroom-type shape. They may be designed to flex or peel away under pressure to open and close. The purpose of the exhaust valve may be to control the direction of flow of the exhaust gases and to keep the surrounding water out of the regulator once the flow of gases has stopped.
Many of the SCUBA second stage regulators exhaust directly into the surrounding water. This may mean that the water is in direct contact with the entire outside surface of the exhaust valve. Most of the second stage regulators may also have the exhaust valve(s) mounted at an angle an in the low point within the regulator housing. This may help to collect any water that has entered the regulator at or near the bottom of the system so that it can be cleared or purged out.
There may be a few reasons that exhaust valves can seep or leak water back into the regulator. One may be under-pressure created during the inhalation cycle. This under-pressure may flex the exhaust valve inward, distorting it against the edge of a circular opening and cross bars, causing it to leak. Another may be a passing flow of water that may catch on the outside sealing edge of the exhaust valve, flexing it open causing it to leak.
There are several reasons for water flow on the outside of the exhaust valve. One may be when the diver enters the water. Most divers enter the water somewhat rapidly, either jumping or sliding into the water. The water may very quickly flood in to the open areas of the bubble deflector. Furthermore, the water may rush in against the outside surfaces of the exhaust valve. The water may catch the edge of the valve and flex it, causing it to leak.
Another reason for water flowing past the exhaust valve may be a laminar flow of water that is created by the exhaust bubbles. Once the exhaust gases travel through the circular opening and past the exhaust valve they may become or create bubbles. Bubbles are naturally buoyant and travel upward toward the surface. As the bubbles are traveling upward they may affect the surrounding water that is in contact with bubbles, drawing the water upward along with them creating a laminar flow of water that may flow on and past the exterior surfaces of the exhaust valve.
Exhaust valves may have been designed to provide low exhaust resistance during heavy breathing rates. This may have resulted in the valves becoming somewhat larger (1″-1.5″ in diameter) or having multiple or several valves. When the diver is breathing at a lower or moderate rate, only the upper portion of the exhaust valve may be used, while the lower portion may remain in the closed position. The laminar flow of water created by the bubbles exiting the top portion of the valve may catch on the lower sealing edge of the exhaust valve causing it to leak.
Seepage or leaking of water via the exhaust valve may be a nuisance at best, and a dangerous situation if diving in contaminated or polluted water.
Another common feature of most of the SCUBA second stage regulators may be a bubble deflector. The bubble deflector may be made of some type of molded rubber or plastic and may be mounted around or next to the exhaust valve(s). The purpose of the bubble deflector may be to capture the exhaust bubbles and divert them away from the front of the diver's face and vision.
Bubble deflectors include bubble exit openings that may be large enough to allow water to enter the lower half of the bubble exit opening, while the bubbles escape out of the top half of the bubble exit opening. The water entering at the lower half of the bubble exit opening may be part of the laminar flow of water that the bubbles create.